Captain’s Plot – September/October 2026

WINTERIZATION

By Ryan Taffett

Where has all the time gone? Another year is winding down and unless you’re in the south or planning to run your boat that way, it’s already time to start preparing for winterization.

Winterization and winter layup isn’t just a function of storage. It’s a critical time to inspect for and prevent damage to your hull, onboard systems, and engines. With that in mind, let’s dive into the best practices to prevent freeze damage and corrosion on your boat.

Winterization should always begin with fresh engine oil and fuel and oil filter changes on both outboards and inboard diesels. Ideally, you will want to run the engines to operating temperature first, as doing so suspends contaminants to better drain them from the system. This also makes the removal of the old oil a much quicker and easier task.

If the oil appears milky in color or has a concerning amount of contaminants or metal shavings in it, this is when you will want to inspect for further damage from water intrusion or accelerated engine wear.

Assuming your old oil is looking good, adding fresh oil is the next step to neutralize the acidic combustion byproducts that corrode bearings during extended storage.

For outboard boats, there is one other key oil to change: the lower unit oil. Drain and refill the lower unit gear lube to check for water intrusion, also indicated by milky colored oil. Additionally, for outboard boats, your engine manufacturer may recommend a fogging process (oil coating) to protect the internal components from corrosion. Finally, run fuel stabilizer through the system prior to wrapping it up for the year.

On diesel inboard-powered boats, you also need to flush your raw water cooling system. To do this you will want to flush with a very low temperature rated nontoxic marine or RV antifreeze (propylene glycol). I prefer to go better than the cheapest minus 50 variants for the best protection.

Run the antifreeze through until the fluid exiting the engine exhaust is the non-diluted color of the antifreeze itself, and repeat the process for onboard generators. While you’re at it, don’t forget to change your generator’s oil and filter too.

Once your engines are all set, or if you plan on running your boat for a few more trips in freezing temperatures before winterizing the engines, it’s time to turn your attention to the water systems onboard. Freezing can not only easily damage your water systems, but in the case of saltwater systems with plastic strainer bowls, it can easily create a real sinking risk. On the freshwater side, drain the water tanks completely, then bypass the water heater to avoid damaging heating elements. Run nontoxic marine or RV antifreeze through every faucet, washdown spigot, transom shower, and head onboard until the fluid runs bright and clear.

If your boat has air conditioning units onboard, be sure to flush the raw water intake pump and manifold with antifreeze. Any trapped water in the heat exchanger coils can rupture their copper lines if it freezes. From here, if you have an ice maker or other appliance that uses water, disconnect the supply line, cycle the solenoid valve to clear residual water, and run antifreeze through the system.

At this point, it’s a good time to do a visual inspection of the boat’s hull and electrical system for damage and functionality. It’s always best to catch any maintenance needs on the front side of the winter season as opposed to the spring when boat yards get busy with launching, and hiring repair labor comes with longer lead times.

Check the hull for blistering and fiberglass damage, as any water intrusion that results in freezing can cause further extensive damage to your hull. If you have an enclosure on your boat, you may also want to consider taking that down and storing it to prevent damage due to high winds, debris, UV and brittleness from freezing temperatures.

If you choose to store your boat in-water for the winter, be sure an appropriate bubbler or de-icer system is deployed in the water around the boat. The theory behind these systems is to force the warmer water upward to prevent the surface water from freezing around the boat. Also be sure to install an ignition protected marine-rated engine room heater to keep the engine and/or bilge area from seeing freezing temps, especially when water can stagnate and freeze around bilge pumps.

Please only use appropriate engine room heaters for this purpose, as regular portable home units cause fires onboard boats regularly.

Once everything onboard looks good, it’s time to cover up the boat. If you have a custom fitted cover, now is the time to install that. If not, you may want to consider shrink wrap as a relatively inexpensive way to protect and preserve your gelcoat, tower metal, and teak decks. Shrink wrap creates a complete weather shield, even against heavy snow, when properly supported and installed. Make sure ventilation is installed along with dehumidification products to prevent mold, mildew, and corrosion throughout the winter. I also like to add a zipper access door to the shrink wrap to get on and off the boat for inspection and maintenance throughout the winter. These doors are great for early spring prep when it’s still cold and windy too.

Overall, taking a comprehensive, system-by-system approach ensures that when spring commissioning arrives, your boat returns to service without costly repairs or missed days on the water. Enjoy the last bit of your season and stay warm!

Ryan Taffet of Stuart, Florida, grew up fishing at the Jersey Shore. When he is not busy as product manager for NAVICO Group, a division of Brunswick Corporation, he’s fishing and boating on his Everglades 240CC Feelin Crabby. The views and opinions expressed in this editorial are only those of Ryan Taffet and do not reflect the views or positions of Brunswick Corporation or its affiliates.